Operation; Precautions; Indicators; Controls - Crown DC-300A II Reference Manual

DC-300A II Power Amplifier

4 Operation

4.1 Precautions

Your amplifier is protected from all external faults. Even
so, you should take the following precautions:
1. When the level of an input source is uncertain,
or an audio component has not been previously
used with your amplifier, always begin with the
level controls at a minimum and gradually in-
crease them while monitoring the output level.
This approach helps avoid loudspeaker blasts.
2. Don't forget, your amplifier does not have a turn
on delay. Beware of turn-on transients from
other equipment ahead of the amplifier—always
turn the amplifier on after other equipment has
stabilized.
3. Turn off the amplifier and unplug it from the AC
mains before replacing the fuse, installing an in-
put sensitivity jumper or changing the position
of the Dual-Mono switch.
4. There are important differences between Dual
and Bridge-Mono mode wiring (refer to Section
3.3.1).
5. Operate the amplifier with the correct fuse: a 5
amp, 250 volt, type MTH fuse for units config-
ured for 200 volt or higher AC mains, and a 10
amp, 250 volt, type AB fuse for units configured
for AC mains of less than 200 volts.
6. Be careful when driving a transformer-coupled
device (such as an electrostatic loudspeaker)
or other loads that appear as a low-frequency
short circuit (less than 3 ohms) without a series
isolating capacitor. Such operation may dam-
age the load and needlessly activate the
amplifier's V-I limiting.
7. Operate the amplifier with AC mains of no more
than 10% above the selected line voltage and at
the specified line frequency (50 to 400 Hz).
8. Never connect the output to a power supply
output, battery or power main. This can cause
electric shock and damage to the amplifier.
9. Do not expose the amplifier to corrosive chemi-
cals such as soft drinks, lye, salt water, etc.
10. Do not tamper with the circuitry. Unauthorized
circuit changes invalidate the warranty.
11. Do not short the ground lead of an output to the
input signal ground or oscillations may result.
12. We recommend that you avoid using the ampli-
fier with frequencies above 30 kHz.

4.2 Indicators

Your amplifier has three front panel indicators. The yel-
low power indicator glows when the amplifier is turned
on and the unit is receiving power.
The IOC (Input/Output Comparator) indicators work
like sensitive distortion meters. Each channel has a red
LED (light emitting diode) that flashes when distortion
of any kind exceeds 0.05%. They typically glow for
about one minute after the AC power is turned off.

4.3 Controls

A power switch and level controls are located on the
front panel. When you power up the amplifier, remem-
ber that the unit does not have a turn-on delay. Each
channel has its own level control which is used to ad-
just the desired output level. Both level controls are
used in Dual mode, but only the channel 1 control
should be used in Bridge-Mono mode.
The amplifier is switched between Dual and Bridge-
Mono operation with the Dual-Mono switch located on
the back panel of the amplifier (see Section 2).
The unit's input gain is 26 dB as determined by 1%
precision resistors in the feedback loop. This can be
changed to a sensitivity of 0.775 volts by following the
instructions in Section 7.

4.4 Protection

Your amplifier is protected against all the common haz-
ards that plague high-power amplifiers, including
shorted, open and mismatched loads; overloaded
power supplies, chain destruction phenomena, input
overload and high-frequency blowups.
Protection against shorted and low impedance loads
is provided by the JTS (Junction Temperature Simula-
tion) circuitry. This circuitry instantaneously limits the
amplifier's output voltage to the maximum safe level for
the output transistors. With a loudspeaker, you can tell
the amplifier has activated load protection because it
causes audible distortion. The noise might be com-
pared to crossover "notch" distortion or a snapping
sound, depending on the load characteristics. Loud-
speaker systems with impedances of 4 ohms or higher
will not activate this system.
All voltage amplification circuitry is designed to limit
current. So in the extremely unlikely event of a device
failure, the amplifier will prevent further damage.
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